The present invention relates to ballistic armor ceramic. More specifically, the present invention pertains to ballistic armor ceramic made from an alpha-beta SiAlON ceramic material that exhibits excellent ballistic performance results, as well as provides other advantages over earlier armor ceramic materials. An alpha-beta SiAlON ceramic material contains an alpha SiAlON phase (which can also be referred to as an alpha-prime SiAlON phase or an α-SiAlON phase or an α′-SiAlON phase) and a beta SiAlON phase (which can also be referred to as an beta-prime SiAlON phase or an β-SiAlON phase or an β′-SiAlON phase). The alpha-beta SiAlON ceramic material may also contain optional intergranular phases such as a glassy phase (which is typically amorphous) and/or a crystalline phase.
Ballistic armor ceramic is intended to be worn by a user for protection, as well as for use in protecting light mobile equipment and vehicles, against high-speed firearm projectiles (e.g., bullets) and fragments (e.g., shrapnel). There are some main considerations concerning protective ballistic armor materials.
One consideration for protective ballistic armor is the weight of the armor. Protective armor for heavy, but mobile, military equipment (e.g., tanks and large ships), is known. Such armor usually comprises a thick layer of alloy steel that has the purpose to provide protection against heavy and explosive projectiles. Because of the large size of this equipment, the greater weight of the alloy steel kinds of armor is not a significant consideration for equipment such as tanks and ships. However, due to its greater weight, such armor is quite unsuitable for light vehicles such as automobiles, jeeps, light boats, or aircraft since armor of greater weight compromises performance. The same is true for body armor worn by a user. In this situation, heavy body armor is undesirable and impractical.
While specifications for body armor and armor for light vehicles may vary upon the specific application, armor suitable for these kinds of applications must prevent penetration of bullets of any weight at high speeds (e.g., speeds in the range of 700 to 3000 meters per second). Further, armor suitable for these kinds of applications must satisfy certain weight limitations (e.g., an armor weight that is acceptable for use on light vehicles varies with the type of vehicle, but generally falls in the range of 40 to 70 kg/m2).
It can thus be appreciated that it would highly desirable to provide a ballistic armor, and especially a ballistic armor ceramic, that is able to satisfactorily prevent penetration of projectiles even when traveling at high speeds. It can also be appreciated that it would be highly desirable to provide such a ballistic armor ceramic that is sufficiently lightweight to not impede the performance of light vehicles or individuals in the case of ballistic ceramic body armor.
The cost of the material is another consideration concerning protective ballistic armor materials. In the case of overly complex armor arrangements, particularly those arrangements depending entirely on synthetic fibers, the armor arrangement comprises a notable proportion of the total vehicle cost. In such a situation, the result can be that manufacture of the vehicle is not profitable due to the cost of the ballistic armor component. It is an appreciation that it would be highly desirable to provide a ballistic armor, and especially a ballistic armor ceramic, that is affordable to make wherein the affordability of the armor results from one or both of the cost of materials and the cost of manufacture of the ballistic armor ceramic.
An additional consideration in armor design is compactness of the ballistic armor bodies or components. A thick armor panel, including air spaces between its various layers, increases the target profile of the vehicle, as well as increases the wind resistance of the vehicle. As can be appreciated, each one of these results is undesirable in that it makes the vehicle more susceptible to compromise to attack by an enemy. In the case of vehicles retrofitted with internal ballistic armor (e.g., civilian automobiles or even military vehicles needing more armor protection), there oftentimes is a lack of space to affix a thick panel to those areas that require protection. It can thus be appreciated that it would be highly desirable to provide a ballistic armor, and especially a ballistic armor ceramic, that presents a compact design so as to take up less space than heretofore thicker armor panels, and thus, be suitable to retrofit existing vehicles.
Heretofore, there have been alpha-beta SiAlON ceramic compositions that include rare earth elements. Although the compositions are different from the present inventive SiAlON ballistic armor ceramic, U.S. Pat. No. 7,309,673 for SIALON CERAMIC AND METHOD OF MAKING THE SAME to Yeckley and owned by Kennametal Inc. of Latrobe, Pa. 15650 discloses an alpha-beta SiAlON ceramic that contains ytterbium and lanthanum. The ceramic material of U.S. Pat. No. 7,309,673 is useful for cutting tool applications. U.S. Pat. No. 7,309,673 is incorporated by reference herein.
Heretofore, potential candidates for use as ballistic armor include ceramic materials. Silicon carbide and boron carbide are two especially suitable ceramic material candidates for ballistic armor ceramic. The following patents describe ballistic armor ceramic materials, as well as other kinds of armor ceramic materials. U.S. Pat. No. 6,805,034 B1 to McCormick et al. pertains to a silicon carbide armor body. U.S. Pat. No. 7,104,177 B1 to Ahajanian et al. discloses a ceramic-rich composite armor. U.S. Pat. No. 7,117,780 to Cohen discloses a composite armor plate.
Further, an earlier co-pending patent application, which is U.S. patent application Ser. No. 11/652,314 filed Jan. 11, 2007 for ALPHA-BETA SIALON BALLISTIC ARMOR CERAMIC by Russell L. Yeckley (and assigned to Kennametal Inc.), which is incorporated herein by reference, pertains to an alpha-beta SiAlON armor ceramic. This patent application discloses specific examples of ballistic armor ceramic. Although the compositions are different from the present inventive SiAlON ballistic armor ceramic, a co-pending U.S. Ser. No. 11/652,314 filed on Jan. 11, 2007 for ALPHA-BETA SIALON BALLISTIC ARMOR CERAMIC by Russell L. Yeckley (and assigned to Kennametal Inc.) discloses a ballistic armor ceramic that comprises alpha-beta SiAlON. In the specific examples, the ceramics include two rare earth elements. One rare earth element is bound to the alpha-SiAlON phase and another rare earth element is not bound to the alpha SiAlON phase. This earlier patent application (i.e., U.S. Ser. No. 11/652,314) discloses two basic starting powder mixtures used to make the alpha-beta SiAlON ceramic material. One starting powder mixture contains the following powders: silicon nitride, aluminum nitride, aluminum oxide, ytterbium oxide, and lanthanum oxide. The other starting powder mixture contains the same components as the first starting powder mixture, but further includes silicon carbide.
Still referring to the specific examples in U.S. Ser. No. 11/652,314, the silicon nitride is present in an amount between about 70.45 weight percent and 83.65 weight percent of the starting powder mixture. The aluminum nitride powder is present in an amount between about 5.95 weight percent and 11.91 weight percent of the starting powder mixture. The aluminum oxide powder is present in an amount between about 1.00 weight percent and 6.95 weight percent of the starting powder mixture. The ytterbium oxide powder is present in an amount between about 8.14 weight percent and 9.95 weight percent of the starting powder mixture. The lanthanum oxide powder is present in an amount between about 0.50 weight percent and 0.77 weight percent of the starting powder mixture. When present, the silicon carbide powder is present in an amount between about 5.00 weight percent and 15.00 weight percent of the starting powder mixture.
Still referring to the specific examples in U.S. Ser. No. 11/652,314, the alpha SiAlON content ranges between about 60.9 weight percent and about 95.4 weight percent of the ceramic body. The beta SiAlON phase content ranges between about 4.6 and about 39.1 weight percent of the ceramic body. The Vickers hardness ranges between about 17.770 and about 20.62. The fracture toughness (KIC) ranges between about 6.500 and about 7.730.
In the specific examples of ballistic armor ceramic in a co-pending U.S. Ser. No. 11/652,314 filed on Jan. 11, 2007 for ALPHA-BETA SIALON BALLISTIC ARMOR CERAMIC by Russell L. Yeckley (and assigned to Kennametal Inc.), the value of “z” ranges between about 0.36 and about 0.96. More specifically, Table A below sets forth the starting powder compositions and the “z” values for Batches Nos. 2833A through 2833D in the co-pending U.S. Ser. No. 11/652,314.
TABLE AStarting Powder Mixtures (in weight percent of the totalstarting powder mixture) of the Batches Nos. 2833A through2833 D and the “z” Value from U.S. Ser. No. 11/652,314BatchSiliconAluminum“z”No.NitrideNitrideAluminaYtterbiaLathinaValue2833A83.655.951.498.140.77.362833B76.219.823.279.920.77.642833C77.609.334.178.140.77.722833D70.4511.916.959.920.77.96
Physical properties of the ballistic armor ceramic are important to satisfactory performance. These physical properties include the hardness, the fracture toughness and the density of the ceramic material. One goal is to achieve a ballistic armor ceramic with a proper combination of the hardness, the fracture toughness and the density to attain satisfactory performance.
Although current ballistic armor ceramic materials may provide satisfactory performance results, there remains a need to provide an improved ballistic armor ceramic whereby such armor addresses the above-mentioned design considerations for ballistic armor. In this regard, the improved ballistic ceramic would be able to satisfactorily prevent penetration of projectiles even when traveling at high speeds, as well as be sufficiently lightweight so as to not impede the performance of light vehicles or individuals in the case of ballistic ceramic body armor.
Further, such improved ballistic armor ceramic would be affordable to make wherein the affordability of the armor results from one or both of the cost of materials and the cost of manufacture of the ballistic armor ceramic. In reference to the method of manufacturing, such improved ballistic armor ceramic would provide the capability to be made into more complex shapes or geometries than heretofore available. This would be due to the ability to make the ceramic by methods (e.g., sinter-HIP techniques) that allow for more flexibility than earlier methods (e.g., hot pressing techniques).
In addition, such improved ballistic armor ceramic would present a compact design so as to take up less space than heretofore thicker armor panels, and thus, be suitable to retrofit existing vehicles. The capability to make ballistic armor ceramic of more complex shapes facilitates activities like the retrofitting of existing vehicles.